Hitting Your Funny Bone at Night

Okay, Jack, listen up. You're a human, which, let's be honest, isn't saying much. Your "funny bone" isn't actually a bone; it's a nerve. When you smack it, it sends weird signals to your brain. The joke plays on the phrase 'dark humor', which is comedy about serious things, and uses the fact that it happens 'at night'. Night and dark makes you think about darkness and it sounds like a darker sense of humor. Get it? Probably not, but a bear can hope.